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Cook Engineering Services : Dynamic Designer

Hands-on engineering is how Greg Cook describes himself and his craft. He is owner and principal of Cook Engineering Services (Glendale, CA), an engineering consulting firm. With many years of experience as a machinist and welder/fabricator before earning his mechanical engineering degree, Greg honed his engineering skills first at Lockheed, and then at Walt Disney Imagineering as a Senior Animation Engineer.

In 1995, Cook hung his shingle as an engineering consultant for theme park designs and the entertainment industry. Since then, he has worked on many exciting projects ranging from vehicles, to aircraft, to animated props, and show action equipment for a myriad of well known organizations.

Cook uses several software packages to create and analyze the designs. "I use SolidWorks for 3D design," says Cook. "I transitioned from a 2D work environment to 3D solids to take advantage of assemblies. Visualization, dynamic and structural analysis, and the ability to check for interference between moving parts are great advantages. Working in 3D is the only way to go in terms of doing animation. Today's 3D CAD packages are affordable, powerful, and reliable."

He also uses Dynamic Designer simulation and optimization software from Mechanical Dynamics (Ann Arbor, MI) that is seamlessly integrated with SolidWorks software to analyze the system dynamics. Cook used to do dynamic calculations by hand. However, when a project has simultaneously moving parts, the analysis process gets tricky. "I can calculate the dynamic loads on individual parts and transfer those loads to the next part, run its dynamics, and figure in the effects of the first part. But that process is time consuming and not as accurate as using Dynamic Designer. The software allows me to analyze the model as a complete working assembly. Dynamic Designer works as the components in the model are moving. The accuracy of the dynamic calculations increases using the software and significantly reduces the time to do the calculations," adds Cook.

"I can build a mechanism in SolidWorks, assign velocity or displacement functions to the linear actuators or electric motors that power the mechanism, and run the simulation in Dynamic Designer. The software is quite easy to make the computer model operate just as my client wants the product to behave in real life. After running the simulation, I can plot the results to document the forces and accelerations generated by the motion profile. These forces and accelerations are used to perform the structural analysis to determine if the structure is going to work successfully and safely. Using Dynamic Designer, I can run the full dynamic profile right on the solid model and then do the stress analysis. Depending on the results, design changes may be required."

While Cook's projects are far from simple, he uses an efficient methodology of addressing assignments. He starts his designs in SolidWorks, moves to Dynamic Designer, and then completes the process using a CAD-based FEA package. "If the stress levels are higher than the allowables, then changes to the geometry of the structural element are made to lower the stresses. That effort may or may not change the weight, center of gravity, or where the pivot points are located. The Dynamic Designer simulation is rerun using the existing motion profile, and followed up with another stress analysis. It's an iterative process," notes Cook.

Past projects that Cook has worked on have been quite complex. Animated figures, for instance, have multiple joints. Ten or more parts can be moving simultaneously. Hydraulic or pneumatic cylinders are typically used to animate different parts of a body or creature depending on the force required. Dinosaurs for example, can have cantilevered structures with more than a dozen segments, measure 21-feet in length, and weigh thousands of pounds. Occasionally in theme parks, moving figures are suspended over a guest's head or move in close proximity to guest. The simultaneous motions going on inside the figure make it complex in terms of dynamics and safety.

Motion Simulator Project Cook Engineering Services first used Dynamic Designer to analyze a motion base simulator that is currently in use today in an urban entertainment center in San Francisco. For this project, the client developed the original concept and preliminary design and produced a working prototype. Cook Engineering Services was asked to bid the dynamic and structural analysis phase of the project. As it turned out, the production company created SolidWorks models of the complete assembly for their use. After winning the bid, Cook was able to calculate the dynamic loads and complete the structural analysis using their finished models, thus saving additional time.

When Cook was awarded the motion simulator work, he performed some preliminary hand calculations. "I was satisfied with the results of my efforts, however, I knew that there were some very complex motions that were occurring within the structure and they were going to be time consuming to calculate by hand."

So, Cook approached his SolidWorks distributor and talked to him about his dynamics needs. "I also went to Mechanical Dynamics' website and looked at their product very carefully. I downloaded the demo software package, ran a couple of test simulations, and was impressed with what I saw. The technology was affordable and it ran on a PC. It just made good sense to purchase it," adds Cook. With the help of Ian Hogg, a Mechanical Dynamics application engineer, Cook was able to get the software up and running quickly while in the midst of the complex project.

During the simulator project, Cook addressed the challenge related to the assembly of the SolidWorks model itself. "I discovered that I needed to change the method of the model assembly to get it into Dynamic Designer because the software distinguishes between moving parts and fixed parts. That issue took a little bit of time to understand how I needed to organize the assembly of the computer model. Once I got that under control, Dynamic Designer was very useful." We were able to provide the client with a complete analysis of the project including electric motor torque's, bearing loads, and vibration analysis of the image projection equipment.

Cook says that he realizes more than a 50% time savings when simulating dynamics problems using Dynamic Designer versus hand calculations. It is much faster and accurate to build a solid model and run a simulation than performing the analysis by hand.

"User accuracy improves using Dynamic Designer," says Cook. "The software allows me to analyze more complex motions with greater accuracy and speed. The other advantage is that it allows me to make changes to the model quite easily and rerun the simulation while minimizing the additional hours for the client. Engineers can make mistakes without even knowing it when using a calculator. Using Dynamic Designer, I can change the model, rerun the simulation, and know that I've removed the human error part of the equation. My results are consistent and that raises my confidence in the integrity of the data."

Since Cook is able to save time using Dynamic Designer, he is able to adhere to tight time constraints. The software allows him to reduce analysis time so that he can out-bid his competition. "If I can complete a job faster and be more productive and accurate, then I can bid less hours," notes Cook. On some jobs, Cook says he out-bids his competition by a factor of two to one.

Author: Laura Carrabine

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Page last modified on February 18, 2000
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